The invention relates to a device for producing images of layers of the interior of a three-dimensional object. A coded image is produced by irradiating the object from a large number of radiation source positions which are situated in one plane. The coded image consists of separate perspective images. Layer images of the object are formed from the coded image by superposition of the perspective images on a photosensitive element. The perspective images are superposed by means of an imaging matrix whose imaging elements are distributed in the matrix plane according to the flat distribution of the radiation source positions.
A device of this kind is known from German Offenlegungsschrift No. 27 46 035. In this Offenlegungsschrift, all perspective images of the coded image are superposed by means of a lens matrix which serves as an imaging matrix. In an image space of the lens matrix there is obtained a three-dimensional brightness distribution which corresponds to the density distribution in the three-dimensional object. When a photosensitive layer, for example, a frosted glass plate, is introduced into this superposition zone, images can be formed of arbitrary layers of the object, also oblique layers, by corresponding positioning or displacement of the radiation sensitive element.
It is a drawback of this method, however, that layers of the object are sharply imaged only if the photosensitive layer is situated within the depth of focus range of the lenses of the lens matrix. Because the depth of focus range of the lenses is limited, only a comparatively small part of the object can be reproduced by sharp layer images in the case of a large reconstructed object volume. Layer images of the object which are situated outside the depth of focus range are blurred. The depth of focus range can be increased by means of diaphragms in front of the lenses, but this causes a loss of brightness.
It is a further drawback of the known decoding device that it produces different layer images in different scales, so that diagnosis of the object on the basis of the layer images is impeded.
German Offenlegungsschrift No. 24 14 322 (corresponding to U.S. Pat. No. 4,023,037) discloses a holographic method for the reconstructing of layer images. In this method, the coded image is irradiated by means of a converging incoherent radiation beam. An image is then formed by combining the coded image, or a superposition of the perspective images, and a hologram which is arranged in the focal plane of a lens. The hologram serves as an imaging matrix in which the radiation source positions of the recording device are stored at a changed scale. For reconstructing different layer images, the coded image is displaced in the radiation beam in the direction of the optical axis. Different layer images of the objects are then reconstructed with different enlargements with respect to each other or with respect to the actual object layers and in different planes.